The temperature dependences of dc magnetization of the two CrI\(_3\)  samples, L and S, are plotted in Fig. REF (c). While both samples show expected transitions from paramagnetic to ferromagnetic, \(T_\mathrm {C}\)  is noticeably smaller in the sample S which was pulverized with ball milling. Contrary to the case of CrCl\(_3\) , in CrI\(_3\) -L we find the maximum of its first derivative is located closer to the previously known Curie temperature at \(T_\mathrm {C}\)  = 61.3 K than the second derivative. We thus use the same method to identify the Curie temperature of CrCl\(_3\) -S at \(T_\mathrm {C}\)  = 35.8 K. Note that this is quite close to the Curie temperature of CrI\(_3\)  in the monolayer limits [1]}. Therefore, we conclude that the effect of ball-milling was in significantly reducing not only the area of van der Waals layers but also the number of stacked layers.
